A mild heat shock at 35 degrees C which induces heat shock gene expression greatly enhances survival following a second shock at a higher temperature in Drosophila larvae, pupae, adults and cell lines. The 35 degrees C treatment is also effective in preventing heat induced developmental defects in pupae. The higher temperatures (40 degrees C) shut down RNA and protein synthesis. The low temperature treatment which induces heat shock protein synthesis speeds up the recovery of both protein and RNA synthesis following the lethal heat shock. We have recently shown that heat shock protein synthesis in Chinese hamster ovary cells associated with acquisition of ability to survive heat treatments that would otherwise be lethal. This suggests that the heat shock response in Drosophila may be similar to that in mammals and may be important for cell survival. The research program described here is designed to use the effects of heating on survival to isolate mutants which will be useful in further study of the functions of heat shock proteins and the regulation of gene expression following heat shock.